The present invention relates to hot water dispensing apparatus, and more particularly a boiling water dispenser capable of maintaining and dispensing large quantities of water at boiling temperature.
It is often desirable for restaurant and other institutional food service applications to have a source of hot water for various cooking purposes, such as preparation of pastas, potatoes, gravies, soups and similar dishes. A constantly available source of heated water, available at near-boiling temperatures on demand is also useful for cleaning purposes. A variety of water heating and dispensing apparatus have been devised to satisfy these applications.
A typical hot water dispenser includes a reservoir in which water is heated by a heating device. A control system senses and maintains the water in the reservoir at a desired temperature. Control systems typically include a temperature sensing probe to monitor the temperature of the water in the reservoir and a level sensing probe to monitor the volume of water retained in the reservoir. Examples of heated water dispensers can be found in U.S. Pat. No. 5,019,690 to Knepler and U.S. Pat. No. 5,038,752 to Anson.
The device in the Knepler '690 patent includes a steam sensing unit which senses the temperature of steam which evolves from the heated water-reservoir. The steam serving unit is position to receive steam from a steam discharge tube which communicates with the reservoir. Steam passes from the reservoir through the tube and exits the tube at the steam sensing unit. A steam sensor of the steam sensing unit is coupled to a control system to activate and deactivate the heating element in response to steam exiting the tube. The steam sensor, coupled with the control unit, maintains the water retained in the reservoir within a desired temperature range.
The Anson '752 patent shows a novel steam sensor mounting structure which facilitates positioning of a steam sensor so as to be responsive to the presence and absence of steam vented from the reservoir of the heated water dispensing apparatus. The sensor mounting structure thermally insulates the sensor from the water reservoir and permits free access of ambient air to the sensor in the absence of venting steam.
The teachings of the Knepler '690 patent are very successful when operating with a tank capacity of approximately five gallons. When the structure of Knepler '690 is employed with a heated water dispensing apparatus having a capacity of ten gallons or more, certain performance parameters may not be satisfied. One problem that may arise with a larger volume of water is that the heating element may prematurely deactivate. The heating element may tend to deactivate when the water in the reservoir is approximately 200 degrees fahrenheit. After a period of time the heating element is once again activated to further heat the water to an acceptable temperature.
After considerable study and research of this problem it has been found that when cold water is heated, air which is otherwise dissolved in the water, comes out of the solution and rises to the top surface whereupon it escapes to the ambient atmosphere. The evolution of gas from solution becomes more rapid as the water temperature increases towards the boiling point. The air escaping from solution is heated although it is not yet heated to boiling temperature or formed steam. Since the escaping air is heated it tends to rush out through the steam discharge tube and past the steam sensor. The volume of heated air in the larger capacity system is sufficient to affect the temperature sensed by the steam sensor to the point where the sensor indicates that the water is at boiling temperature when, in fact, this is not the case.
The ten gallon tank, due to its increased capacity, has a larger interior volume than the five gallon tank and is typically designed to be deeper and have a larger top surface area than the five gallon tank. As a result of the dimensional differences between the ten gallon reservoir and the five gallon reservoir, and the substantially large volume retained therein, a sufficient quantity of heated air flows across the steam sensor thereby prematurely deactivating the heating element.
For the forgoing reasons, there is a need for an apparatus which has a substantially larger heated water volume capacity which employs a novel and non-obvious boiling water control system to maintain the temperature of the water retained in the reservoir at or near the boiling temperature for water.